Various electronic devices, such as semiconductor devices, and photonic devices, such as lasers and solar devices, may include or may desirably include germanium-tin layers, such as GeSn, GeSiSn, and the like. For example, GeSn layers can be used to form direct band gap devices and/or may be used to provide strain in an adjacent germanium layer to increase mobility in the germanium layer. Similarly, GeSiSn layers can be used to form tunable band gap devices as well as optical devices having tunable optical properties. To obtain the desired device properties, the germanium-tin films generally have a crystalline structure, which generally follows the crystalline structure of the underlying layer.
GeSn layers may be deposited or grown using a variety of techniques. For example, vacuum processes, including molecular beam epitaxy and ultra-high vacuum chemical vapor deposition, have been used to form GeSn films. The germanium precursor for such processes typically includes digermane (Ge2H6) or trigermane (Ge3H8). When the film includes silicon, the silicon precursor may include a disilane, trisilane, or other higher order silane compounds, or hetero-nuclear Si—Ge compounds with the general formula of (H3Ge)xSiH4-x (x=1-4), (H3Si)xGeH4-x (x=1-4).
Although such processes have been used to deposit or grow crystalline GeSn and GeSiSn layers, use of digermane, trigermane, or higher order germane precursors is problematic in several respects. For example, formation of films or layers including GeSn using digermane or higher order germane precursors, such as trigermane, is not selective when certain carrier gasses (e.g., hydrogen) and/or dopants (e.g., p-type dopants) are used with the precursor. Also, digermane is relatively unstable (explosive) in concentrated form; as a result, an amount of the precursor contained in a vessel may be limited, typically to less than 154 grams, which in turn, causes throughput of processes using such a precursor to be relatively low. In addition, digermane and higher order germanes are relatively expensive. Accordingly, improved processes for forming crystalline films including GeSn are desired.